Additional example configuration for phpMyAdmin

with the PMA_HOST and PMA_PORT and PMA_ARGITRARY defined it seems that the intent is to have the system leverage this connection information, however with out the PMA_USER and the PMA_PASSWORD configuration set this information is not used, to better serve the example the db user and pass from  lines 25 and 26 could be set here and then the container would auto login for phpMyAdmin for the example

Author: randallmorse

basics/installation/environments/docker.md

@@ -344,6 +344,8 @@ services:
         PMA_HOST: some-mysql
         PMA_PORT: 3306
         PMA_ARBITRARY: 1
+        PMA_USER: root
+        PMA_PASSWORD: admin
       restart: unless-stopped
       ports:
         - 8081:80